Validation of the Technology
Bioimpedance analysis has been "calibrated" most frequently against either
densitometry or isotope dilution as the "gold standard". Most commercial
machines are supplied with proprietary prediction equations the details of
which are hidden from the user within the software of the machine. In addition,
many prediction algorithms have been published in the bio-medical press. All
prediction equations include height, as a surrogate measure for the inter-
electrode distance, but may also include, weight, sex or age as variables.
Many studies have been undertaken not only to validate particular prediction
equations but also to identify other variables which may improve the quality
of the predictor. The overall precision of any given prediction equation is the
sum
of the precisions associated with each independent variable. Typically,
standard errors of the estimate (SEE) for total body water are of the order of
3-10%, slightly higher for lean body mass. It must be stressed that inevitably
prediction equations are population-specific. The user must be assured that the
predictor chosen is appropriate for their particular subject cohort.